Steven M. Madey

A laboratory model to evaluate cutout resistance of implants for pertrochanteric fracture fixation.

Objectives: To establish a laboratory model of implant cutout, which can evaluate the effect of implant design on cutout resistance in a clinically realistic “worst case” scenario. Setting: Orthopaedic biomechanics laboratory. Design: Implant cutout was simulated in an unstable pertrochanteric fracture model, which accounted for dynamic loading, osteoporotic bone, and a defined implant offset. For model characterization, lag screw cutout was simulated in human cadaveric specimens and in polyurethane foam surrogates. Subsequently, foam surrogates were used to determine differences in cutout resistance between 2 common lag screws (dynamic hip screw, Gamma) and 2 novel blade-type implant designs (dynamic helical hip system, trochanteric fixation nail). Main Outcome Measures: Implant migration was continuously recorded with a spatial motion tracking system as a function of the applied loading cycles. In addition, the total number of loading cycles to cutout failure was determined for specific load amplitudes. Results: Implant migration in polyurethane surrogates closely correlated with that in cadaveric specimens, but yielded higher reproducibility and consistent cutout failure. The cutout model was able to delineate significant differences in cutout resistance between specific implant designs. At any of 4 load amplitudes (0.8 kN, 1.0 kN, 1.2 kN, 1.4 kN) dynamic hip screw lag screws failed earliest. The gamma nail lag screw could sustain significantly more loading cycles than the dynamic hip screw. Of all implants, trochanteric fixation nail implants demonstrated the highest cutout resistance. Conclusions: Implant design can significantly affect the fixation strength and cutout resistance of implants for pertrochanteric fracture fixation. The novel cutout model can predict differences in cutout resistance between distinct implant designs.

Locked plating of distal femur fractures leads to inconsistent and asymmetric callus formation.

Objectives: Locked plating constructs may be too stiff to reliably promote secondary bone healing. This study used a novel imaging technique to quantify periosteal callus formation of distal femur fractures stabilized with locking plates. It investigated the effects of cortex-to-plate distance, bridging span, and implant material on periosteal callus formation. Design: Retrospective cohort study. Setting: One Level I and one Level II trauma center. Patients: Sixty-four consecutive patients with distal femur fractures (AO types 32A, 33A-C) stabilized with periarticular locking plates. Intervention: Osteosynthesis using indirect reduction and bridge plating with periarticular locking plates. Main Outcome Measurement: Periosteal callus size on lateral and anteroposterior radiographs. Results: Callus size varied from 0 to 650 mm2. Deficient callus (20 mm2 or less) formed in 52%, 47%, and 37% of fractures at 6, 12, and 24 weeks postsurgery, respectively. Callus formation was asymmetric, whereby the medial cortex had on average 64% more callus (P = 0.001) than the anterior or posterior cortices. A longer bridge span correlated minimally with an increased callus size at Week 6 (P = 0.02), but no correlation was found at Weeks 12 and 24 postsurgery. Compared with stainless steel plates, titanium plates had 76%, 71%, and 56% more callus at Week 6 (P = 0.04), Week 12 (P = 0.03), and Week 24 (P = 0.09), respectively. Conclusions: Stabilization of distal femur fractures with periarticular locking plates can cause inconsistent and asymmetric formation of periosteal callus. A larger bridge span only minimally improves callus formation. The more flexible titanium plates enhanced callus formation compared with stainless steel plates.

Far Cortical Locking Can Reduce Stiffness of Locked Plating Constructs While Retaining Construct Strength

BACKGROUND Several strategies to reduce construct stiffness have been proposed to promote secondary bone healing following fracture fixation with locked bridge plating constructs. However, stiffness reduction is typically gained at the cost of construct strength. In the present study, we tested whether a novel strategy for stiffness reduction, termed far cortical locking, can significantly reduce the stiffness of a locked plating construct while retaining its strength. METHODS Locked plating constructs and far cortical locking constructs were tested in a diaphyseal bridge plating model of the non-osteoporotic femoral diaphysis to determine construct stiffness in axial compression, torsion, and bending. Subsequently, constructs were dynamically loaded until failure in each loading mode to determine construct strength and failure modes. Finally, failure tests were repeated in a validated model of the osteoporotic femoral diaphysis to determine construct strength and failure modes in a worst-case scenario of bridge plating in osteoporotic bone. RESULTS Compared with the locked plating constructs, the initial stiffness of far cortical locking constructs was 88% lower in axial compression (p < 0.001), 58% lower in torsion (p < 0.001), and 29% lower in bending (p < 0.001). Compared with the locked plating constructs, the strength of far cortical locking constructs was 7% lower (p = 0.005) and 16% lower (p < 0.001) under axial compression in the non-osteoporotic and osteoporotic diaphysis, respectively. However, far cortical locking constructs were 54% stronger (p < 0.001) and 9% stronger (p = 0.04) under torsion and 21% stronger (p < 0.001) and 20% stronger (p = 0.02) under bending than locked plating constructs in the non-osteoporotic and osteoporotic diaphysis, respectively. Within the initial stiffness range, far cortical locking constructs generated nearly parallel interfragmentary motion. Locked plating constructs generated significantly less motion at the near cortex adjacent to the plate than at the far cortex (p < 0.01). CONCLUSIONS Far cortical locking significantly reduces the axial stiffness of a locked plating construct. This gain in flexibility causes only a modest reduction in axial strength and increased torsional and bending strength.

Charnley total hip arthroplasty with use of improved techniques of cementing. The results after a minimum of fifteen years of follow-up.

Three hundred and fifty-seven consecutive Charnley total hip arthroplasties were performed in 320 patients with use of a so-called second-generation technique of cementing between July 1976 and June 1978. This technique includes use of a distal femoral intramedullary cement plug, hand-mixing of the cement, and use of a cement gun to deliver the cement into the femoral canal in a retrograde fashion. At the time of the latest follow-up evaluation, a minimum of fifteen years after the arthroplasty, 130 patients (142 hips) were still alive, 189 patients (214 hips) had died, and one patient (one hip) had been lost to follow-up. A radiograph was made for 116 (82 per cent) of the 142 hips in the 130 surviving patients. Of the 356 hips that had not been lost to follow-up, thirty-three (9 per cent) had had a revision and two (1 per cent), a Girdlestone resection arthroplasty during the follow-up period. Nineteen hips (5 per cent) were revised because of aseptic loosening of the femoral or acetabular component, or both (two hips); seven (2 per cent), because of loosening with infection; and seven (2 per cent), because of dislocation. The two resection arthroplasties were performed because of loosening with infection; both were done in patients who died before the time of the latest follow-up evaluation. Of the 142 hips in the 130 patients who were alive at a minimum of fifteen years, twenty-two (15 per cent) had been revised: fifteen (11 per cent), because of aseptic loosening; three (2 per cent), because of loosening with infection; and four (3 per cent), because of dislocation. Revision of the femoral component because of aseptic loosening (excluding components that were revised because of dislocation or infection) was performed in four (1 per cent) of the entire series of 356 hips and in three (2 per cent) of the 142 hips in the 130 patients who survived for at least fifteen years. Two of the 356 hips and two of the 142 hips had aseptic loosening of the acetabular as well as the femoral component at the time of the revision. Loosening of the femoral component, defined as aseptic loosening leading to revision or as definite or probable radiographic loosening, occurred in ten (3 per cent) of the 356 hips and in six (5 per cent) of the 116 hips for which radiographs were made at a minimum of fifteen years. The acetabular component was revised because of aseptic loosening in seventeen (5 per cent) of the entire series of 356 hips and in fourteen (10 per cent) of the 142 hips in the 130 patients who survived for at least fifteen years. The acetabular component loosened without infection in forty-one (12 per cent) of the 356 hips and in twenty-six (22 per cent) of the 116 hips for which radiographs were made at a minimum of fifteen years. In two of these patients, the femoral component was also revised. Thus, of the entire series of 356 hips, two had a revision of the femoral component alone because of aseptic loosening; fifteen, a revision of the acetabular component alone; and two, a revision of both components. Of the 142 hips in the 130 patients who survived for at least fifteen years, one was revised for loosening of the femoral component alone; twelve, for loosening of the acetabular component alone; and two, for loosening of both components. These findings demonstrate long-term durability of fixation of the femoral component but less reliable fixation of the acetabular component, even when the surgeon is experienced and improved techniques of cementing are used.

Far cortical locking can improve healing of fractures stabilized with locking plates.

BACKGROUND Locked bridge plating relies on secondary bone healing, which requires interfragmentary motion for callus formation. This study evaluated healing of fractures stabilized with a locked plating construct and a far cortical locking construct, which is a modified locked plating approach that promotes interfragmentary motion. The study tested whether far cortical locking constructs can improve fracture-healing compared with standard locked plating constructs. METHODS In an established ovine tibial osteotomy model with a 3-mm gap size, twelve osteotomies were randomly stabilized with locked plating or far cortical locking constructs applied medially. The far cortical locking constructs were designed to provide 84% lower stiffness than the locked plating constructs and permitted nearly parallel gap motion. Fracture-healing was monitored on weekly radiographs. After the animals were killed at week 9, healed tibiae were analyzed by computed tomography, mechanical testing in torsion, and histological examination. RESULTS Callus on weekly radiographs was greater in the far cortical locking constructs than in the locked plating constructs. At week 9, the far cortical locking group had a 36% greater callus volume (p = 0.03) and a 44% higher bone mineral content (p = 0.013) than the locked plating group. Callus in the locked plating specimens was asymmetric, having 49% less bone mineral content in the medial callus than in the lateral callus (p = 0.003). In far cortical locking specimens, medial and lateral callus had similar bone mineral content (p = 0.91). The far cortical locking specimens healed to be 54% stronger in torsion (p = 0.023) and sustained 156% greater energy to failure in torsion (p < 0.001) than locked plating specimens. Histologically, three of six locked plating specimens had deficient bridging across the medial cortex, while all remaining cortices had bridged. CONCLUSIONS Inconsistent and asymmetric callus formation with locked plating constructs is likely due to their high stiffness and asymmetric gap closure. By providing flexible fixation and nearly parallel interfragmentary motion, far cortical locking constructs form more callus and heal to be stronger in torsion than locked plating constructs.

Noninvasive reduction of open-book pelvic fractures by circumferential compression.

Objectives To determine the efficacy and optimal application parameters of circumferential compression to reduce external rotation-type pelvic fractures. Design Biomechanical investigation on human cadaveric specimens. Setting Biomechanics laboratory. Intervention Partially stable and unstable external rotation injuries of the pelvic ring (OTA classification 61-B1 and 61-C1) were created in seven human cadaveric specimens. A prototype pelvic strap was applied subsequently at three distinct transverse levels around the pelvis. Circumferential pelvic compression was induced by gradual tensioning of the strap to attempt complete reduction of the symphysis diastasis. Main Outcome Measurements Pelvic reduction was evaluated with respect to strap tension and the strap application site. The effect of circumferential compression on intraperitoneal pressure and skin–strap interface pressure was measured. Results A successive increase in circumferential compression consistently induced a gradual decrease in symphysis diastasis. An optimal strap application site was determined, at which circumferential compression most effectively yielded pelvic reduction. The minimum strap tension required to achieve complete reduction of symphysis diastasis was determined to be 177 ± 44 Newtons and 180 ± 50 Newtons in the partially stable and unstable pelvis, respectively. Conclusions Application of circumferential compression to the pelvic soft tissue envelope with a pelvic strap was an efficient means to achieve controlled reduction of external rotation-type pelvic fractures. This study derived application parameters with direct clinical implication for noninvasive emergent management of traumatic pelvic ring disruptions.

Effects of Construct Stiffness on Healing of Fractures Stabilized with Locking Plates

The benefits of locked-plate fixation, which include improved fixation strength in osteoporotic bone1-3 and the ability to provide a more biologically friendly fixation construct4,5, have led to the rapid adoption of this technology. Biological fixation of comminuted fractures with locking plates relies on secondary fracture-healing by callus formation6,7, which is stimulated by interfragmentary motion in the millimeter range8,9. Secondary bone-healing can be enhanced by active or passive dynamization10,11. Conversely, bone-healing can be suppressed by rigid fracture fixation aimed at preventing interfragmentary motion12. Biomechanical studies have suggested that locked-plate constructs are stiff and suppress interfragmentary motion to a level that may be insufficient to reliably promote secondary fracture-healing1,13-15. Recent clinical studies substantiate the concern that the inherently high stiffness of locked-plate constructs suppresses callus formation, contributing to a nonunion rate of up to 19% seen with periarticular locking plates16,17. Deficient healing may also contribute to late hardware failures seen with locking plates18-20 since, in the absence of osseous union, constructs remain load-bearing and eventually fail by hardware fatigue or loss of fixation. This paper summarizes a line of research that addresses two questions of critical importance when using locked-plate constructs: 1. Does the high stiffness of locked-plate constructs suppress callus formation and fracture-healing? 2. Can a stiffness-reduced locked-plate technique, termed far cortical locking , improve fracture-healing, compared with standard locked plating, by providing flexible fixation and parallel interfragmentary motion? First, we will present the findings of biomechanical and clinical studies of the effect of construct stiffness on interfragmentary motion and fracture-healing with locking plates. Subsequently, studies that describe the function, benefits, and clinical application of far cortical locking are …

Emergent management of pelvic ring fractures with use of circumferential compression.

Circumferential compression of the pelvis has been recommended for emergent stabilization of open-book pelvic fractures to reduce the risk of life-threatening hemorrhage 1-3. However, little information on the application, effectiveness, and safety of this procedure is available to date 3,4. We therefore investigated noninvasive stabilization of pelvic ring fractures in three cadaveric biomechanical studies. First, we established optimal application parameters for circumferential compression of open-book pelvic fractures. Second, we derived the amount of pelvic stabilization that can be achieved by application of a novel pelvic sling that provides for controlled circumferential compression. Finally, we determined whether this pelvic sling could be applied safely at the emergency scene, where the specific pelvic fracture pattern is not readily assessable. The results of this research demonstrate that circumferential compression with this noninvasive pelvic sling is an effective and safe method for reducing and stabilizing open-book pelvic fractures at the emergency scene. Application Parameters: A cadaveric study was performed to determine the most effective application site and the force required to reduce open-book pelvic fractures. Partially stable and unstable open-book pelvic fractures (Young-Burgess type-II and III anteroposterior compression fractures associated with a 50 and 100-mm diastasis of the symphysis pubis, respectively) were created sequentially in seven nonembalmed human cadavers from individuals with an average age at death of 80 ± 7 years, an average height of 170 ± 9 cm, and an average weight of 74 ± 8 kg Fig. 1 . An experimental pelvic sling consisting of a 50-mm wide, flexible, nonelastic belt was designed. This sling was applied at three distinct …

A Nonlocking End Screw Can Decrease Fracture Risk Caused by Locked Plating in the Osteoporotic Diaphysis

BACKGROUND Locking plates transmit load through fixed-angle locking screws instead of relying on plate-to-bone compression. Therefore, locking screws may induce higher stress at the screw-bone interface than that seen with conventional nonlocked plating. This study investigated whether locked plating in osteoporotic diaphyseal bone causes a greater periprosthetic fracture risk than conventional plating because of stress concentrations at the plate end. It further investigated the effect of replacing the locked end screw with a conventional screw on the strength of the fixation construct. METHODS Three different bridge-plate constructs were applied to a validated surrogate of the osteoporotic femoral diaphysis. Constructs were tested dynamically to failure in bending, torsion, and axial loading to determine failure loads and failure modes. A locked plating construct was compared with a nonlocked conventional plating construct. Subsequently, the outermost locking screw in locked plating constructs was replaced with a conventional screw to reduce stress concentrations at the plate end. RESULTS Compared with the conventional plating construct, the locked plating construct was 22% weaker in bending (p = 0.013), comparably strong in torsion (p = 0.05), and 15% stronger in axial compression (p = 0.017). Substituting the locked end screw with a conventional screw increased the construct strength by 40% in bending (p = 0.001) but had no significant effect on construct strength under torsion (p = 0.22) and compressive loading (p = 0.53) compared with the locked plating construct. Under bending, all constructs failed by periprosthetic fracture. CONCLUSIONS Under bending loads, the focused load transfer of locking plates through fixed-angle screws can increase the periprosthetic fracture risk in the osteoporotic diaphysis compared with conventional plates. Replacing the outermost locking screw with a conventional screw reduced the stress concentration at the plate end and significantly increased the bending strength of the plating construct compared with an all-locked construct (p = 0.001).

Operative chest wall fixation with osteosynthesis plates.

Blunt chest wall trauma is a major cause of morbidity and mortality, especially in the presence of a flail chest where paradoxical inward movement of the flail segment in inspiration is found. Patients with a flail chest require aggressive pain control, pulmonary toilet, and often intubation and mechanical ventilation to establish an internal pneumatic stabilization of the flail segment. This may result in a prolonged ICU stay and pulmonary complications including pneumonia, septicemia and barotrauma. The high mortality rate of up to 10 –36% –12 is partly due to the high prevalence of associated life-threatening extra-thoracic injuries. However, one principle cause of death consists of pneumonia and sepsis with prolonged intubation. Several potential advantages of operative chest wall stabilizations have been reported. These include reduced duration of mechanical ventilation, shortened ICU stay and hospitalization, and decreased likelihood of clinically significant long-term respiratory dysfunction and skeletal deformity. Despite the advantages of operative chest wall fixation, little consensus on the fixation technique exists. This report describes three cases of flail chest injury managed by operative stabilization with plates and screws. The criteria for surgical intervention in this trauma center are traumatic loss of 30% of pleural cavity volume, inability to wean an awake patient from the ventilator, inability to control chest wall pain despite epidural catheter, major air leak or major bleeding, or unstable sternal fracture with overlap. In all three cases a standard posterolateral thoracotomy was performed. The serratus anterior was retracted anteriorly and the latissimus dorsi was divided. To reach more cranially a small portion of the trapezius and the rhomboids were transected in cases 2 and 3. The chest was always entered and hematoma was removed. Pelvic, mandibular and customized reconstruction plates were used, with bending stiffness ranging from 1,936 over 414 to 56 kN mm, respectively. In addition to documentation of the technique, this report describes the results obtained with three distinct osteosynthesis plates and provides a historic overview of alternative fixation means.